Unfinished Business

By Neil Savage

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The apparent discovery of the Higgs boson means that what physicists have long suspected about how the universe is put together appears to be correct. “Now the Standard Model is complete,” says Sheldon Glashow, University Professor and professor of physics and one of the architects of the model. “Complete and unsatisfactory.”

The model describes the subatomic particles and the associated forces, such as electromagnetism, that make up the universe, and predicted the existence of the particles that were subsequently found. The last of these particles was the Higgs boson. But Glashow calls the model unsatisfactory because it requires certain mathematical values to be tuned with exquisite care. Physicists were hoping the Large Hadron Collider’s (LHC) high energy, which produced the Higgs boson, might also turn up other particles that could ameliorate this problem. But none was found.

One possible outcome some physicists expected was evidence of supersymmetry, which posits that each of the known particles has a sort of twin, a selectron for the electron, a sneutrino for the neutrino, and so on. The LHC has found no evidence of those, although there may yet be hope when the collider starts up again at higher energy levels. “I would say things are looking bad for supersymmetry,” Glashow says, adding, “Some would disagree.”

Glashow won the Nobel Prize in Physics in 1979. He was one of three physicists who figured out that two of the four fundamental forces of the universe, electromagnetism and the weak nuclear force, were actually manifestations of one force, the electroweak force. But oddly, the particles involved are not symmetrical; particles that carry the weak force, the W and Z bosons, have mass, while photons, which carry the electromagnetic force, are massless. The theory that Glashow laid out required the existence of either the Higgs boson or something unidentified to explain that breaking of symmetry.

Now, with all the previous predictions met, Glashow is trying to devise the experiments that particle physicists should be doing to go beyond the Standard Model, both to simplify it and to address issues it doesn’t cover, notably the existence of gravity. He recently published a paper in the physics online archive arXiv.org, “Particle Physics in the United States, a Personal View,” suggesting some research American scientists might pursue. He’s also become president of the scientific council for the Mesoamerican Centre for Theoretical Physics, which is being created in Chiapas, Mexico, to expand physics research and education in Central America.

The United States no longer operates equipment at the frontier of high-energy research, with the Tevatron at Fermilab shut down in 2011 and the Superconducting Super Collider, which would have been more powerful than the LHC, terminated by Congress in 1993. But Glashow still sees potential for useful research. “There are all kinds of things we could do that have a chance of revolutionary discoveries,” he says.